Unless you are further processing the 2 Channels so each side is different this will mostly make your panorama more narrow. If the source material is mono then this should result in a mono signal. If it is stereo it should move the edges closer to the center. In either case, depending on your Pan Law settings, this can also increase the final signal level which typically sounds ābetterā to us humans.
Can only recommend āWiderā to expand mono or narrow sources. It does kind of a Haas effect, but magically without causing any phase issuesā¦itās free:
For the master bus i sometimes use K-Stereo by UAD, very subtly though.
IMO it depends on your source audio. In other words, the tool or process will depend on what you want to widen.
For synths, sometimes as mentioned above, recording a 2nd track as close to the 1st, then panning for big and lush and definitely not fake.
If you want to subtly āthickenā vocals, very common in the last decade, and I mean not even close to chorus effect, and not microshifting, I use Cloner and sometimes Stage 1 after it. Chris Selim has a great tutorial explaining Cloner and vocals.
Electric guitars, a ton of tools.
S1 can work for a lot of material, but if you push it very far, I would suggest listening in a mastering room for unnatural artifacts. The same goes for Brainworks BX Stereomaker. A bit more subtle than S1 and Stereomaker would be Bob Katz Precision K Stereo which still gets quite a bit of use here.